The primary components of a drive train of a motor vehicle are a drive unit and a transmission. A transmission provides a speed-power conversion and thus converts the supply of traction force of the drive unit. The invention concerns a process for operating a drive train, which comprises at least one transmission and a hybrid drive as drive unit with an internal combustion engine and an electric machine that can be operated as an electric motor and/or generator.
FIG. 1 shows a drive train diagram of a drive train known from the state of the art having a hybrid drive comprising an internal combustion engine 1 and an electric motor 2, wherein a transmission 4 is connected between the electric motor 2 of the hybrid drive and an output 3 of the drive train. The transmission 4 is an automatic transmission, in which the gear changes or shifts are preferably carried out with an interruption of traction force. A clutch 5, which is disengaged during purely electric motor-based driving in order to decouple the internal combustion engine 1 from the output 3, is connected between the internal combustion engine 1 and the electric motor 2 of the hybrid drive. A drive train such as this typically comprises furthermore either a starting element located in the interior of transmission, which is not shown, or a starting element located outside of the transmission, which is not shown. Such a drive train is also referred to as parallel hybrid drive train.
FIG. 2 shows a diagram, which illustrates the mode of operation known from the state of the art for carrying out a shift in the drive train shown in FIG. 1. In FIG. 2 are shown three torque trends over the time t, namely a time torque trends 6 of a torque that can be transmitted by the clutch 5 connected between the internal combustion engine 1 and the electric motor 2 is shown as a dashed line, a time torque trend 7 of a torque made available by the internal combustion engine 1 is shown as a solid line, and a time torque trend 8 of a torque made available by the electric motor 2 is shown as a dash-dotted line, each specifically during a gear change in the form of a traction shift when the electric motor 2 is operated as a generator.
It is thus apparent from FIG. 2 that in order to carry out a shift in the automatic transmission 4 with previously engaged clutch 5, first the load at the internal combustion engine 1 is reduced (see torque trend 7), and simultaneously the load at the electric motor 2 is reduced (see signal trend 8), while in addition also the torque transmitted by the clutch 5 is reduced according to the signal trend 6. According to FIG. 2, the load made available by the internal combustion engine 1, or the torque made available by the internal combustion engine 1, and the load made available by the electric motor 2, or the torque made available by the electric motor 2, each have a value of zero at the time t1, while the torque that can be transmitted by the clutch 5 amounts to zero only later at time t2. According to the state of the art, the clutch 5 is accordingly disengaged with time delay at time t2 in order to reduce the load at the internal combustion engine 1 and at the electric motor 2, while a gear change is carried out in the automatic transmission between the times t2 and t3. The gear change is completed in the transmission 4 at time t3, while the torque that can be transmitted by the clutch 5 (see signal trend 6) is again built up at time t3. The loads or torques at the internal combustion engine 1 (see signal trend 7) and at the electric motor 2 (see signal trend 8) are again built up delayed in time starting at time t4, according to signal trends 7 and 8.
In the mode of operation of FIG. 2 known from the state of the art for operating a parallel hybrid drive train having an automatic transmission 4, the shift in the transmission 4 is carried out accordingly during the time span Δt23, but the duration of an interruption of traction force at the output 3 corresponds to the time span Δt14. The duration of the interruption of traction force Δt14 accordingly comprises the duration Δt23 for gear change in the automatic transmission 4, plus the duration until the clutch 5 can be opened at time t2 after the reduction in load at the internal combustion engine 1 and at the electric motor 2 at time t1, and plus the time frame until the clutch 5 can transmit torque after the shift time span t3 has been carried out and torque has built up at the internal combustion engine at time t4.
Based on this state of the art, there is a need for a process for operating a drive train comprising a hybrid drive and an automatic transmission, wherein the interruption of traction force at the output can be shortened.